Based on many years experience, the well proven Swiss Tunnel Seismic Prediction System TSP has been substantially augmented for online geological prognosis in underground construction. In its latest version, the Integrated Seismic Imaging System ISIS provides high resolution seismic images of the rock mass around a tunnel face via an array of standard anchor rods. These rods contain 3D-geophones at their tips and can be readily installed during excavation work. A further innovative component of the system is the newly developed high-power repetitive source for application in hard rock: a pneumatic hammer with laser triggering to be mounted on construction machinery. A user-friendly software package permits online data acquisition and processing, 3D-visualization, and a first geological interpretation. Tomographic images of compressional and shear wave velocity fields at fault zones in metamorphic rock of the Gotthard Base Tunnel in the Central Alps are presented.

Das langjahrig bewahrte Schweizer Tunnelseismische Vorauserkundungssystem TSP wurde inzwischen wesentlich weiterentwickelt. In seiner neuen Version, dem Integrierten Seismischen Imaging System ISIS, ermöglicht es hochauflösende seismische Abbildungen des Gebirges im Vorfeld und Umfeld einer Tunnelauffahrung mit Hilfe einer Anordnung von Felsankern, die an ihren Spitzen 3-Komponenten-Geophone enthalten. Eine weitere Neuerung von ISIS ist die pneumatische Hochleistungs-Impulsquelle mit Laser-Triggering. Eine benutzerfreundliche, interaktive Software ermöglicht die online Datenerfassung und -auswertung, 3D-Visualisierung und eine erste geologische Interpretation. Tomografische Abbildungen von Kompressions- und Scherwellengeschwindigkeitsfeldern an Störungszonen in metamorphem Gestein des Gotthard- Basistunnels werden gezeigt.

Base sur de nombreuses annees d'experience, le système suisse, bien etablit, de reconnaissance sismique à l'avancement des tunnels (système TSP), a ete sensiblement ameliore pour obtenir une prevision geologique en temps reel durant l'avancement de travaux souterrains. Sa dernière version, le Système Integre d'Imagerie Sismique (ISIS), fournit des images sismiques haute-resolution du massif rocheux à l'avant d'un tunnel grace à un reseau de tiges d'ancrage standard. Ces tiges, equipees à leur extremite de geophones 3 composantes, s'installent très aisement durant les travaux d'excavation habituels. Le element d'innovation recente concern le nouvelle source très repetitive et de forte puissance pour les applications aux roches dures: un marteau pneumatic-que declenche par un système à laser. Un ensemble de programmes informatiques convivial permet l'acquisition et le traitement en temps reel des signaux et produit une vue 3D ainsi qu'une première interpretation geologique. Nous presenterons des images de reflexion d'ondes de compression et de cisaillement ainsi que des inversions tomographiques de zones de faille dans des terrains metamorphiques obtenues à l'occasion du creusement du tunnel de base du Gothard, dans les alpes centrales.

Introduction

A major factor in driving a tunnel is prior knowledge of the geological environment and the geotechnical parameters to be expected. An increasing extent of underground construction work needs to be carried out under difficult soil and rock conditions. Besides exploratory drilling, nondestructive geophysical methods may be used to indicate lithological heterogeneities within distances of up to several hundred meters. Seismic imaging, with its large prediction range and high resolution, is the most effective method.

Since the early nineties, the Tunnel Seismic Prediction system TSP of Amberg Measuring Technique AG, AMT Switzerland, has been applied successfully in tunnelling projects worldwide (Dickmann, Th. & Sander, B.K. 1996; Sattel, G. et al. 1992). The concept of the Integrated Seismic Imaging System ISISwas developed by the GeoForschungsZentrum Potsdam, GFZ, in cooperation with AMT as a follow-up.

ISIS components

The components of ISIS are the receiver rods, a pneumatic impact source, and a user-friendly software package.

Geophone anchors

Mounting the receiver system can be readily integrated in the tunnel working routine. Standard glass-fiber-reinforced polymer resin anchors are used as housing for 3Dgeophones (Figure 1). The anchor rods act as seismic antennas and simultaneously as stabilizing elements (Borm, G. et al., 1999).

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